Cells of the immune system recognize and are activated by conserved pathogen associated molecular patterns (PAMPs) in infectious agents. The unmethylated CpG dimers embedded in bacterial DNA, as well as certain synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG sequences (termed a CpG motif) that emulated them, are more frequent in the genomes of bacteria and viruses than vertebrates. Recent studies suggest that immune recognition of these motifs may contribute to the host's innate immune response (Klinman et al., Proc. Natl. Acad. Sci. USA 93: 2879, 1996; Yi et al, J. Immun. 157: 5394, 1996; Liang et al., J. Clin. Invest. 98:1119, 1996; Krieg et al., 374 Nature 374: 546, 1995).
In mice, CpG DNA induces proliferation in almost all (>95%) of B cells and increases immunoglobulin (Ig) secretion. This B-cell activation by CpG DNA is T-cell independent and antigen non-specific. In addition to its direct effects on B cells, CpG DNA has also been shown to activate cells of the immune system (see, for example, International Patent Applications WO 95/26204, WO 96/02555, WO 98/11211, WO 98/18810, WO 98/37919, WO 98/40100, WO 98/52581, PCT/US98/047703, and PCT/US99/07335; U.S. Pat. No. 5,663,153).
Although bacterial DNA and certain oligonucleotides can induce a murine immune response, little is known about the immunostimulatory capacity of these materials for the human immune system (Ballas et al., 157 J. Immun. 157: 1840 1996). In addition, differences in the responsiveness of human and murine B cells to certain stimuli render it difficult to extrapolate results obtained from mouse to man.
In view of the above, there exists a need for oligonucleotides that induce an immune response in humans. In addition, there is a need for methods utilizing CpG containing oligonucleotides in the treatment of human diseases.